View Source Boundaries & Access Control

Boundaries is Bonfire's flexible framework for full per-user/per-object/per-action access control. It makes it easy to ensure that users may only see or do what they are supposed to.

users-and-circles

Users and Circles

Ignoring any future bot support, boundaries ultimately apply to users.

Circles are a way of categorising users. Each user has their own set of circles that they can add to and categorise other users in as they please.

Circles allow a user to categorise work colleagues differently from friends, for example. They can choose to allow different interactions from users in the two circles or limit which content each sees on a per-item basis.

verbs

Verbs

Verbs represent actions that the user could perform, such as reading a post or replying to a message.

Each verb has a unique ID, like the table IDs from pointers, which must be known to the system through configuration.

permissions

Permissions

Permissions can take one of three values:

  • true
  • false
  • nil (or null to postgresql).

true and false are easy enough to understand as yes and no, but what is nil?

nil represents no answer - in isolation, it is the same as false.

Because a user could be in more than one circle and each circle may have a different permission, we need a way of combining permissions to produce a final result permission. nil is treated differently here:

leftrightresult
nilnilnil
niltruetrue
nilfalsefalse
trueniltrue
truetruetrue
truefalsefalse
falsenilfalse
falsetruefalse
falsefalsefalse

To be considered granted, the result of combining the permissions must be true (nil is as good as false again here).

nil can thus be seen as a sort of weak false, being easily overridden by a true, but also not by itself granting anything.

At first glance, this may seem a little odd, but it gives us a little additional flexibility which is useful for implementing features such as blocks (where false is really useful!). With a little practice, it feels quite natural to use.

acls-and-grants

ACLs and Grants

An ACL is "just" a collection of Grants.

Grants combine the ID of the ACL they exist in with a verb id, a user or circle id and a permission, thus providing a decision about whether a particular action is permitted for a particular user (or all users in a particular circle).

Conceptually, an ACL contains a grant for every user-or-circle/verb combination, but most of the permissions are nil. We do not record grants with nil permissions in the database, saving substantially on storage space and compute requirements.

controlled-applying-boundaries-to-an-object

Controlled - Applying boundaries to an object

An object is linked to one or more ACLs by the Controlled multimixin, which pairs an object ID with an ACL ID. Because it is a multimixin, a given object can have multiple ACLs applied. In the case of overlap, permissions are combined in the manner described earlier.